1. Field of the Invention
The present invention relates to a sealed storage battery. More specifically, the present invention pertains to a storage battery for stationary applications, such as a lead acid storage battery, which is composed of a large number of cells and used over a long time.
2. Description of the Prior Art
Sealed, stationary lead acid storage batteries have widely been applied to backup power sources for telephone switchboards and computers, power sources for emergency lighting in buildings, and power sources for equipment of receiving and distributing electricity and transforming stations. Since such power sources are required to have a high voltage and a large capacity, it is desirable that each storage battery has a high voltage and a large capacity. Increased dimensions of electrode plates worsen the efficiency of current collection and increase the deflection of the plates in use. In storage batteries used over a long time, increased number of stacked plates makes it rather difficult to manufacture a battery case or container having a desired mechanical strength that can maintain at a constant level the stacking pressure of the plates, which significantly affects the life of the battery and its performance.
A lead acid storage battery shown in FIG. 20 has conventionally been used for such applications. This lead acid storage battery includes a monoblock container, in which two cell rows, each including two cells, are arranged in parallel to each other. The monoblock container 80 includes a first cell row 81 having cells 81a and 81b and a second cell row 82 having cells 82a and 82b, which are arranged in parallel to each other. The monoblock container 80 is sealed with a one-piece cover. The respective cells are separated by intercell partitions disposed in the container and on the cover. Each cell has a positive electrode terminal and a negative electrode terminal provided on the upper surface of the cover. The negative electrode terminals of the cells 81a and 81b included in the first cell row 81 are connected by a connecting bar 83 embedded in a compound packed in a recess formed on the upper surface of the cover.
When these batteries are applied for a power source device, adjacent cells included in different cell rows are electrically connected in parallel in each battery, whereas the respective batteries are electrically connected in series. A power source device having a high voltage and a large capacity can be prepared by connecting a plurality of battery groups in series and/or in parallel, each battery group consisting of a plurality of batteries connected in series.
In the battery discussed above, the respective cells 81a, 81b, 82a and 82b are independent of one another. In case that the characteristics of the respective cells, especially, their capacities, are varied in use, an excess load is applied to a specific cell having the smallest capacity. This further shortens the life of the specific cell. Selection of adequate terminals is required to allow all the four cells included in one battery to participate in discharging. When a large number of batteries are connected with one another, special care is required to select the right terminals.